Pre-exposure prophylaxis (PrEP) 86% effective in reducing HIV among MSM

25 February 2015
An HIV ribbon

The use of antiretroviral treatment (ART) as a pre-exposure prophylaxis (PrEP) has been shown to be 86 percent effective in preventing new HIV infections among men who have sex with men (MSM), and 96 percent effective with serodifferent couples, when the HIV positive partner is also on ART. These new figures were presented yesterday, on the second day of the Conference on Retroviruses and Opportunistic Infections (CROI) 2015 in Seattle, and give further evidence to the effectiveness of PrEP in preventing HIV among at-risk groups.

Of the three studies presented, two looked at PrEP among MSM. The UK PROUD study enrolled 545 men, and started off as a pilot study with a planned expansion to include 5,000 participants. They organised the participants into two arms – the first arm would receive PrEP straight away, whilst the second arm would be deferred for a year. The researchers anticipated an HIV incidence among the deferred arm to be between two to three percent each year, however they found a higher than expected incidence of 8.9 percent. Compared to the 1.3 percent HIV incidence in the arm that was receiving ART, this equates to a statistically significant PrEP effectiveness of 86 percent. The researchers had originally hypothesised that PrEP would only work in a closely monitored cohort with a placebo, however they soon found this to be untrue. Professor McCormack stated: "We found that our concerns about PrEP being less effective in the real world were completely unfounded." After the success, all trial participants were put on PrEP.

The French and Canadian IPERGAY study examined the efficacy of event-driven PrEP among 450 MSM enrolled in the trial. They wanted to ascertain if ART was effective if only taken around the time of possible exposure to HIV, with men asked to take four antiretroviral tablets – two before and two after the sex event. They found that PrEP reduced risk of HIV by 86 percent, the same results as the PROUD study. This was achieved at a high adherence, with roughly half the number of pills than if the men had taken them every day. The study offers another option for at-risk MSM, as they can take PrEP in such a way that was safe and suitable for their lifestyle.

The Partners PrEP Demonstration Project examined the impact of PrEP among serodifferent couples – relationships where one partner is HIV positive and the other partner is HIV negative. They found that when the HIV negative partner was on PrEP and the HIV positive partner was on treatment, the risk of HIV infection was reduced by 96 percent. The conference has not only yielded positive results. Disappointing news came in the form of results from the South African FACTS 001 vaginal microbicide gel trial. It is known that vaginal microbicides can be effective in reducing HIV, if woman are able to use it. However, results from the trial show that there are many barriers to women using it consistently, either because they forget, or because they simply are not in a position to use it. The trial was unable to overcome these barriers and was ineffective in preventing new HIV infections. The trial only highlights the need to find suitable prevention solutions for young and at-risk woman.

UNAIDS Executive Director Michel Sidibé welcomed the new research from the trials, he stated: “These new results are a significant breakthrough in advancing efforts to provide effective HIV prevention options to men who have sex with men and to serodiscordant couples. The results are timely and important and will advance global efforts to end the AIDS epidemic by 2030.”

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